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Dynamics of holomorphic transformations; Mandelbrot and Julia sets.

22 votes
Accepted

Poincaré metric on the Riemann sphere minus more than two points

Yes. The density of the Poincare metric with respect to the spherical metric is a positive continuous function which tends to infinity at the punctures. Thus it is bounded from below by some positive …
Alexandre Eremenko's user avatar
18 votes
Accepted

Can the topologist's sine curve be realized as a Julia set?

The answer is negative. Since every neighborhood of a point on the Julia set is mapped onto the whole Julia set by some iterate of the rational function, it follows that if a small piece of the Julia …
Alexandre Eremenko's user avatar
17 votes
Accepted

On entire functions with polynomial Schwarzian derivative

The answer is this: $$f(z)=\int_{z_0}^z e^{Q(\zeta)}d\zeta,$$ where $Q$ is a polynomial, and this is the general form of an entire function whose Schwarzian is a polynomial. The crucial fact that $f$ …
Alexandre Eremenko's user avatar
16 votes

The deep significance of the question of the Mandelbrot set's local connectedness?

MLC is indeed a very technical and complicated counterpart of a simple question which arises from the general theory of dynamical systems. For a generic system (in a given finitely-parametric family) …
Alexandre Eremenko's user avatar
14 votes

On complex dynamics in high dimensions

Main areas are dynamics of automorphisms (for example, Henon maps), dynamics of endomorphisms, dynamics of foliations, and local dynamics. Eric Bedford, Tien-Cuong Dinh, John Fornaess, Misha Lyubich, …
Alexandre Eremenko's user avatar
13 votes

How is the Julia set of $fg$ related to the Julia set of $gf$?

Answer. $J(fg)$ is the full $g$-preimage of $J(gf)$. (And vice versa with interchange of $f$ and $g$). Proof. Let $A=fg$ and $B=gf$. Then we have a semi-conjugacy $gA=Bg$. Now it is a general fact, …
Alexandre Eremenko's user avatar
11 votes

If I have zeros at the vertices of an icosahedron, where should the poles go?

MR1032073 Doyle, Peter; McMullen, Curt, Solving the quintic by iteration. Acta Math. 163 (1989), no. 3-4, 151–180.
Alexandre Eremenko's user avatar
10 votes

Who proved that the Mandelbrot set's Julia sets are locally connected?

Nobody. This is the principal unsolved problem in the area, which is called MLC (That the Mandelbrot set is locally connected). Two Fields medals were awarded for partial progress in this problem. Ab …
Alexandre Eremenko's user avatar
10 votes
Accepted

Does the Mandelbrot set have dense interior?

The answer is positive and this is not difficult (a normal families argument). The boundary of the Mandelbrot set is the set of $J$-instability. Every point $c_0$ of this set is a limit of $c_n$ such …
Alexandre Eremenko's user avatar
8 votes

Periodicity in iterated powers of sin, cos, exp

You iterate the function $a\mapsto (\cos a)^z$ which is ill defined for complex $a$ and $z$; you need a branch cut, which is visible on some of your pictures. In holomorphic dynamics, usually entire f …
Alexandre Eremenko's user avatar
8 votes
Accepted

Ahlfors' proof of Bloch's theorem

He explains his choice in lines 8-9 on p. 364 of the paper: "This metric has the curvature $-4$ for it is obtained from the hyperbolic metric by the transformation $w'=w^{1/2}$ ." Remarks. By more sop …
Alexandre Eremenko's user avatar
7 votes

Convergence of Newton's method

Your statement that iterates of the Newton method converge to a cycle almost everywhere is equivalent to the statement that for every polynomial $f$ the Julia set of the rational function $z-f(z)/f'(z …
Alexandre Eremenko's user avatar
7 votes
Accepted

Smooth Julia set for quadratic polynomials

The answer to a) is yes, and this was proved by Fatou in 1919. Sur les équations fonctionnelles Bulletin de la S. M. F., tome 48 (1920), p. 208-314. There are many generalizations of this fact. For o …
Alexandre Eremenko's user avatar
7 votes
Accepted

Power series expansion of the Koenigs function

You do not tell the crucial thing: how large is $|f'(0)|$. There is no simple expression for coefficients or any other simple expression for $h$, even when $f$ is quadratic polynomial $\lambda z+z^2$. …
Alexandre Eremenko's user avatar
6 votes

Is there an (almost) dense set of quadratic polynomials which is not in the interior of the ...

Yes, these are the neighborhoods of certain Misiuriewicz points, see for example the right picture in the bottom here: http://classes.yale.edu/fractals/MandelSet/MandelBoundary/Mis.html
Alexandre Eremenko's user avatar

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